In the design of suspension system, there are two competing concerns. The first concern is that the ride be "soft" in order to obtain maximum comfort for the driver, as well as to prevent damage to cargo, for instance. Thus, tractor-trailer combinations utilize air suspension systems in order to achieve this "soft" ride. The second competing concern is that the vehicles be able to corner well without substantially displacing the center of gravity of the vehicle in order to maintain vehicle roll stability. Therefore, it is desirable that the suspension be relatively "soft" in the vertical direction and yet stiff in roll in order to provide good cornering characteristics.
U.S. Pat. No. 4,667,974, issued to Giese, is directed towards a vehicle suspension system designed to provide high roll stability and a soft ride. The details of this patent are incorporated herein by reference thereto.
Suspensions sometimes employ rubber or other elastomeric vertical bushings. These bushings generally are uniform in height and horizontal cross section thickness. These bushings thus react to loads generally equally in all horizontal and angular directions.
Suspensions usually provide one set of damping devices, such as shock absorbers, that dampen only one type of axle motion. This allows other types of axle motion to occur undampened or not optimally dampened.